The invention relates to the field of integrated circuit (IC) design. Specifically, it relates to a programmable DC voltage generator system for a semiconductor chip.
A semiconductor memory unit of an integrated circuit (IC) system is typically arranged in an array of cells, where each cell stores a small charge representing one bit of information (1 or 0). In a memory unit such as a dynamic random access memory (DRAM) system, each cell of the array requires periodic refreshing, since the small charge stored in the cell tends to leak off due to several factors, such as an increase in the temperature of the chip. Accordingly, a DRAM system is provided with circuitry for performing a refresh operation for refreshing the cells of the DRAM array, as well as for other operations such as read and write operations.
The purpose of a DC voltage generator system on a semiconductor chip is to provide power regulation and power conversion, such as for converting a voltage provided by an external power supply to an appropriate voltage level for performing an operation executed by the chip. For example, in a conventional DRAM chip, an on-chip DC voltage generator system is used to convert a voltage supplied by an external power supply to many different voltage levels so that each different voltage level is appropriately converted for effectively supporting the various DRAM operations.
Typical components included in a DC voltage generator system for a memory system, such as a DRAM system, are a Vpp pump system for supporting boosted wordline operations to enhance access time; a Vbb pump system for biasing the body of transfer devices included in the memory array so that the subthreshold leakage of each cell of the array is minimized for insuring cell retention of a stored voltage; and a Vneg pump system for holding unselected wordlines to a predetermined negative voltage, so that transfer gates having a lower Vt may be implemented in the array, resulting in a performance gain, while maintaining low leakage.
The DC voltage generator system may further include reference voltage supply components, including a bandgap reference voltage, Vbgr, which is a constant voltage level insensitive to the supply voltage, temperature and process, used to provide a reference voltage for other circuit components; a DC voltage reference, Vrefdc, which is a voltage level that varies proportionately with the supply voltage, used for generation of a voltage proportional to the supply voltage; and a constant current reference, IREF, used as a reference for biasing analog circuits to be used such as differential amplifiers.
Each voltage pump system of the DC voltage generator system outputs a fixed voltage, thus a different pump system is used for outputting each of the generated voltages, i.e., Vneg, Vpp, and Vbb. Each pump system is custom designed to output the desired voltage, thus contributing to high manufacturing costs. Further, more than one a customized pump system is generally required for each of the voltages Vneg, Vpp, Vbb for satisfying each different operational mode, such as testing modes, active operation mode, stand-by mode and power-up mode, further increasing manufacturing and design costs, and consuming space on the chip.
A voltage pump system is disclosed in U.S. Pat. No. 5,818,766, entitled xe2x80x9cDrain Voltage Pump Circuit for Nonvolatile Memoryxe2x80x9d, in which the pumping rate of the pump system is tuned during an initial pumping interval by a control circuit according to a relative difference between an output voltage level and a target voltage level. Once the target voltage level has been reached by the voltage pump system, the output voltage level and pumping speed are kept constant. The target voltage level is determined by resistor components of the control circuit. Therefore, the target voltage level is a fixed voltage level. It is not possible to change the target voltage level or to selectably adjust the output voltage level and pumping speed of the voltage pump system once the target voltage level has been reached.
Accordingly, a need exists for a programmable DC generator system for enabling and controlling at least one voltage pump system to output a selectable and variable voltage level for operating a DRAM system.
An aspect of the present invention is to provide a programmable DC voltage generator system having a programming circuit for controlling at least one voltage pump system of the DC voltage generator system to output and maintain a range of voltage levels for operating a DRAM system in different modes.
It is still another aspect of the present invention to provide an on-chip programmable DC voltage generator system capable of being programmed after being installed in a system such as a DRAM system.
Accordingly, a programmable DC voltage generator system is provided for driving at least one voltage pump system for generating pump voltages, such as Vbb, Vneg and Vpp, where each pump voltage operates a DRAM system during different modes, such as sleep, stand-by and active modes.